The current Universe is composed by a mixture of relativistic species , baryonic matter , dark matter and dark energy which evolve in a non-trivial way at perturbative level .
A successful description of the cosmological dynamics should include non-standard features beyond the simplistic approach idealized by the standard cosmology in which cosmic components do not interact , are adiabatic and dissipationless .
We promote a full perturbative analysis of linear scalar perturbations of a cosmological model containing baryons , dark matter and a scalar field allowing for the presence of relative entropic perturbations between the three fluids .
We show that tiny departures from a constant scalar field equation of state w _ { S } = -1 damage structure formation in a non-acceptable manner .
Hence , by strongly constraining w _ { S } our results provide compelling evidence in favor of the standard cosmological model and rule out a large class of dynamical dark energy models .

PACS numbers : 98.80.-k , 95.36.+x , 04.25.Nx